1. Field of the Invention
This invention relates to a semiconductor package in which a semiconductor chip is die-bonded on a plastic substrate and sealed by a sealing resin, and a method of fabricating the semiconductor package.
2. Description of the Prior Art
Demand for plastic ball grid arrays (BGA) has recently been increased for satisfaction of requirements of high densification, high-speed operation and an increase in the number of pins. FIG. 2 shows a conventional plastic BGA package. As shown, the plastic BGA package comprises a semiconductor chip 12 die-bonded on an upper surface of a plastic substrate 11 by an adhesive 13 such as an Ag paste and overmolded with a sealing resin 14. A number of solder balls 15 serving as connecting electrodes are bonded to the backside of the plastic substrate 11. When the plastic BGA package is mounted on a circuit substrate, the solder balls 15 are bonded to pads of the circuit substrate by means of reflow soldering. Since the overall plastic BGA package is heated in a reflow furnace in a reflow soldering process, moisture or water content in the package is vaporized such that the vapor pressure is increased. As a result, a portion of the plastic substrate 11 on which the chip is mounted swells downward (popcorning phenomenon) or a joint between the sealing resin 14 or the semiconductor chip 12 and the plastic substrate 11 is separated (delamination).
To overcome the popcorning phenomenon and the delamination, U.S. Pat. No. 5,296,738 discloses a semiconductor package in which a plastic substrate has through vent holes vertically extending through a die-bonding area thereof. In the reflow soldering process, moisture vapor produced in the package is released through the vent holes. However, this construction results in a problem that an adhesive agent such as the Ag paste flows through the vent holes when the semiconductor chip is die-bonded to the plastic substrate by the adhesive agent.
As a countermeasure, U.S. Pat. No. 5,612,576 has proposed to close the vent holes by closing caps at the backside of the substrate. In this case, however, the adhesive agent flows into the vent holes through the upper open ends thereof in the die-bonding process, thereby clogging the vent holes. Thus, the adhesive agent prevents moisture vapor produced in the package during the reflow heating from passing through the vent holes. Consequently, the proposed construction reduces effects preventing the popcorning phenomenon and the delamination.